THE SPLEEN. 435 
coalescing to form the hepatic duct, which opens into the duodenum. 
The secretion of bile is entirely from the venous blood, and the hepatic 
artery is solely destined to nourish the gland. The nerves are chiefly 
from the sympathetic system, a few small branches being derived from 
the pneumogastric through the solar plexus. The horse has no gall 
bladder like the cow, as well as the human species. 
THE FUNCTION of the liver is doubtless chiefly of a depuratory nature, 
but the soapy nature of the bile seems to be destined to aid in dissolving 
the fatty materials which are contained in the food, and to stimulate the 
intestines to perform their duties. 
THE SPLEEN, 
THE SPLEEN can scarcely be considered as a gland, inasmuch as it has 
no excretory duct, but it contains within its substance a number of little 
bodies, called Malpighian corpuscles, which most probably perform the 
same office as the absorbent glands. Its weight as compared with the 
whole body is about the same as in man, whose spleen weighs six ounces, 
while that of the horse rarely exceeds three pounds. It is attached by 
the lesser omentum (a fold of the peritoneum) to the stomach (see fig. 3, 
page 430), and occupies the left side of that organ. It is covered by a 
serous coat continuous with the peritoneum, and its internal structure is 
spongy, and made up of cells which contain a large quantity of blood. 
THE FuNcTION of the spleen is not positively ascertained, but it is 
believed to perform the office of a reservoir for the blood required by the 
stomach, with which it is closely connected by a set of vessels (vasa brevia), 
and also to effect some change in the blood itself. 
THE PANCREAS. 
THE PANCREAS is an elongated gland resembling in structure the 
salivary glands, placed close to the spine, above the stomach. It has two 
excretory ducts, which carry the pancreatic fluid secreted by it into the 
duodenum through a valvular opening common to it and the hepatic 
duct. Tur use of the pancreatic fluid appears to be similar to that of 
the saliva. 
THE KIDNEYS. 
THE KIDNEYS are two oval organs situated beneath the psoas muscles, 
and only retained in their position by the fatty cellular membrane which 
envelops them, and by the upward pressure of the other abdominal viscera 
below them. The right kidney is completely within the ribs, but the 
left scarcely advances at all beyond the eighteenth rib: each averages 
about forty ounces in weight, but there is a considerable variation in size 
and form. Unlike the corresponding organ in the cow, the horse’s kidney 
is not split up into lobules, though there is some little irregularity ot 
outline and surface, as may be seen in the atnexed figure, which was 
taken from a specimen somewhat remarkable in these respects. A trans- 
verse section shows the internal structure, which is composed of a central 
cavity, the pelvis, into which the urine flows, and from which it is carried 
to the bladder by the ureter. In this pelvis several conical projections 
are .visible, having minute openings around their apices, which are the 
terminations of the tubuli uriniferi composing the substance of the inter- 
nal part of the organ. The external is the true secreting portion, and in 
FF2 
